In the field of integrated circuit fabrication, wet chemical etching processes are widely used, to selectively etch regions in the successive layers of an integrated circuit, to form electronic components and conductors from the various layers of materials. One problem which arises when such wet chemical etching is used is that the etchant solution often will, at the microscopic levels of interest, exhibit substantial non-uniformity of concentration. Localized regions of low chemical concentration of the etchant may occur due to low mobility of the active elements of the solution, causing so-called "dead spots." These dead spots may also be the result of the etchant solution becoming saturated within localized regions. When this happens, the etching action is diminished in spots and overall is non-uniform. One obvious way to increase local concentrations is to increase the overall concentration of the etchant solution. This, however, does not resolve the problem of non-uniformity of concentration and may result in a solution which is so strong as to increase the etching rate in some areas to the point of producing undesireable effects, such as substantial undercutting of photoresist and resulting loss of control over geometrical considerations (e.g., line resolution and spacing). Another approach is to place in the etching bath a magnetic bead or beads which can be moved through the application of a magnetic field, to produce a stirring action. Magnetic bead stirring, though, creates vortices which aid macroscopic mixing without substantially changing the non-uniformity of etchant concentration at microscopic levels. Significant dead spots still result with magnetic bead stirring.
Accordingly, it is an object of the present invention to provide a method of wet chemical etching for use in integrated circuit fabrication, wherein dead spots are substantially alleviated.
Another object of the present invention is to provide a method of wet chemical etching for use in integrated circuit fabrication, to improve the uniformity of the etching rate over the surface of the material to be etched.
A further object of the invention is to provide a wet etching process which avoids undercutting photoresist or other materials.
Still another object of the invention is to provide a wet etching process which allows use of weaker etching solutions.